The present invention relates generally to a drive system of an apparatus for transporting substrates through a chemical mechanical polishing system.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, it is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly non-planar. This non-planar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a xe2x80x9cstandardxe2x80x9d or a fixed-abrasive pad. A standard polishing pad has durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles, if a standard pad is used, is supplied to the surface of the polishing pad.
The carrier heads that hold the substrates are conventionally mounted on a movable carrier support structure. For example, the Mirra(trademark) chemical mechanical polisher, available from Applied Materials, Inc., includes a carousel that supports four carrier heads. Typically, the carrier support structure can transport each carrier head and the substrate attached thereto between a first position, where the substrate is loaded or unloaded from the carrier head, and a second position, where the substrate is polished.
One problem that has been discovered is that the forces generated on the carrier head during polishing by a moving polishing pad can cause the entire support structure to move or vibrate. These vibrations can disrupt the polishing process, thereby creating non-uniform polishing rates across the substrate and introducing defects.
In one aspect, the invention is directed to a chemical mechanical polishing apparatus. The apparatus has a polishing station, a transfer station, a carrier head to support a substrate, a rotatable carousel supporting the carrier head, a carousel drive shaft coupled to the carousel to rotate the carousel, and a carousel drive system. The carousel is rotatable between a first position in which the carrier head is in the polishing station and a second position in which the carrier head is in the transfer station. The carousel drive system includes a drive motor, a gear reduction box coupled to an output of the drive motor, and a brake system coupling the gear reduction box to the drive shaft.
Implementations of the invention may include one or more of the following features. The brake system may include a rotor coupled to a lower end of the drive shaft. A central portion of the rotor may be coupled to the drive shaft, and frictional force may be applied to a perimeter portion of the rotor when braking the drive shaft. The perimeter portion of the rotor is gripped between a first ring and second ring during braking. An actuator may press the first ring against the perimeter portion of the rotor. An annular middle portion of the rotor may connect the perimeter portion to the central portion. The annular middle portion of the rotor may be sufficiently thin so as to flex to permit the perimeter portion to undergo vertical motion. A support plate may be secured in a parallel and spaced-apart arrangement with the second ring, with the perimeter portion of the rotor positioned between the support plate and the first ring. A clamp disk may be positioned between the rotor and the support plate. The clamp disk may have a central portion secured to a support plate and a perimeter portion that forms the second ring. The clamp disk may include an annular middle portion connecting the perimeter portion to the central portion, the annular middle portion being sufficiently thin so as to flex to permit the perimeter portion of the clamp disk to undergo vertical motion. A plurality of springs may urge the second ring toward the perimeter portion of the rotor.
In another aspect, the invention is directed to a drive system for a carrier head support structure in a chemical mechanical polishing apparatus. The drive system has a drive shaft to be coupled to carrier head support structure, a drive motor, a gear reduction box coupled to an output of the drive motor, and a brake system coupling the gear reduction box to the drive shaft.
Potential advantages of implementations of the invention may include zero or more of the following. Less backlash, play and flexibility in a gear reduction box is transmitted to a drive shaft of a carrier head support structure. Thus, vibration and motion of a carrier head support structure, such as a multi-head carousel, can be reduced during polishing. This can improve polishing uniformity, decrease defects, and increase yield.
Other advantages and features of the invention will be apparent from the following description, including the drawings and claims.